1. Field of the Invention
The present invention relates to a dual backset deadbolt assembly, more particularly to a dual backset deadbolt assembly which has a simplified construction and which is easier to operate for adjusting between longer and shorter backset lengths.
2. Description of the Related Art
U.S. Pat. No. 4,639,025 discloses an adjustable deadbolt assembly which includes a bolt casing that houses a bolt, an extension housing fixed to a rear end of the bolt casing, a crank plate mounted in the extension housing, an adjustable bolt extension member connected to a rear end of the bolt and housed in the extension housing, a disengaging pin, and crank plate holding means. The extension housing is formed with an oblong pin hole. The crank plate is to be connected to a spindle for transmitting the actuation of the spindle to the bolt, and is turnable about an axis to move the bolt between a locking position and a releasing position. The bolt extension member includes a fixed plate member and an extensible channel member pivoted to the fixed plate. The extensible channel member is formed with a longitudinal guide aperture which has front and rear engaging portions. A pivot pin extends through the fixed plate member and the guide aperture in the extensible channel member, and is movable along the guiding aperture for engaging selectively the front and rear engaging portions. The disengaging pin extends through the oblong pin hole in the extension housing, and is movable along the oblong pin hole for disengaging the pivot pin from the front or rear engaging portion. The crank plate holding means is mounted movably in the extension housing to hold the crank plate in a movable position so that the crank plate can be kept in a cooperative relationship with the extensible channel member. The crank plate holding means is formed with front and rear notches. The disengaging pin engages the front notch when the pivot pin engages the front engaging portion of the guide aperture, and engages the rear notch when the pivot pin engages the rear engaging portion of the guide aperture. To adjust the backset length of the deadbolt assembly, the disengaging pin is moved upward in the oblong pin hole using one hand of the user to disengage from the front or rear notch and to disengage the pivot pin from the front or rear engaging portion of the guide aperture. Then, the crank plate holding means is pulled backward or pushed forward using the other hand of the user, with said one hand of the user holding the disengaging pin. As such, the adjustment operation requires both hands of the user, and is inconvenient to conduct. Moreover, with the use of the disengaging pin, which is movable along the oblong pin hole, for disengaging the extensible channel member and the crank plate holding means from the longer or shorter backset position, the aforesaid deadbolt assembly has a relatively complicated structure which unavoidably results in an increase in the manufacturing and assembly costs.
Therefore, the main object of the present invention is to provide a dual backset deadbolt assembly which has a simplified construction and which is easier to operate for adjusting between longer and shorter backset lengths.
Accordingly, the dual backset deadbolt assembly of the present invention includes a deadbolt housing, a deadbolt, an extension housing, a crank retainer, a transmission plate, a linking plate, a biasing spring, and a crank member. The deadbolt housing has a front end and a rear end opposite to the front end in a longitudinal direction. The deadbolt is mounted in the deadbolt housing, and is movable along the longitudinal direction between an extended position and a retracted position relative to the front end of the deadbolt housing. The extension housing is fixed to the rear end of the deadbolt housing. The extension housing has two parallel side plates which are connected to each other so as to confine a slide chamber with an open front end. Each of the side plates has first and second backset holes displaced from each other along the longitudinal direction. The crank retainer is disposed slidably in the slide chamber, and includes an upper actuating member which has a top wall that extends along the longitudinal direction and that is exposed from the extension housing. The top wall is formed with first and second positioning holes which are displaced from each other along the longitudinal direction. The top wall is further formed with an actuating aperture. The crank retainer further includes a lower holding member disposed below the actuating member. The holding member has two side panels which are parallel to the side plates of the extension housing and which are formed with aligned crank retaining holes. The transmission plate has a front end fixed to the deadbolt. The linking plate has a front end connected pivotally to the front end of the transmission plate so as to be pivotable about a horizontal axis transverse to the longitudinal direction, and a rear end which extends into the crank retainer so as to be disposed below the top wall of the actuating member and which is formed with an upward positioning projection. The biasing spring biases the rear end of the linking plate upward so as to engage the positioning projection with one of the first and second positioning holes in the top wall of the actuating member, thereby aligning the crank retaining holes with one of the first and second backset holes in the extension housing. The crank member, which is sandwiched between the side panels of the holding member, has a lower end portion retained rotatably in the crank retaining holes and formed with a spindle engaging hole that is aligned with the crank retaining holes, and an upper end formed with an actuating protrusion which projects upwardly through the actuating aperture in the top wall of the actuating member so as to engage the actuating member. The crank member is adapted to be coupled co-rotatably with the deadbolt operating spindle when the deadbolt operating spindle is inserted into the spindle engaging hole. Rotation of the crank member causes the actuating protrusion to move the actuating member along the longitudinal direction, thereby moving the linking plate and the transmission plate along the longitudinal direction relative to the extension housing, and thereby moving the deadbolt between the extended and retracted positions. The positioning projection is depressible against biasing action of the biasing spring for retracting into said one of the first and second positioning holes so as to permit the crank retainer to be moved along the longitudinal direction relative to the extension housing in order to enable the positioning projection to engage the other one of the first and second positioning holes and in order to align the crank retaining holes with the other one of the first and second backset holes, thereby permitting adjustment of the deadbolt assembly between longer and shorter backset lengths.